The present invention relates to apparatus for transferring cryogenic fluids such as liquid oxygen or liquified natural gas (LNG), and especially relates to a cryogenic fluid dispensing system and method for transferring the cryogenic fluid to a vehicle through fixed and flexible cryogenic pipes.
It is well known that transferring stored cryogenic fluids from storage tanks to a point of utilization of the fluid requires specialized apparatus because such cryogenic fluids as liquified oxygen, hydrogen, nitrogen, argon or LNG must be stored and maintained at extremely low temperatures. For example, LNG is normally stored at temperatures of between -240.degree. Fahrenheit (F.) to -200.degree. F. (about -150.degree. Celsius (C.) to -130.degree. C.). It is hoped that LNG will someday become an economical, clean and abundant fuel to power conventional vehicles such as trucks and automobiles. Some governments (e.g., California) have already implemented legislation to require a phase-in of use of LNG for such purposes in the near future.
Efficient and safe storage, distribution and use of LNG poses many technical problems inherent to processing such low temperature fluids. For example, pipes transferring LNG from typically underground storage tanks must be insulated to restrict heat input to the fluid from the environment. Most such cryogenic pipes utilize an inner line for transferring the fluid, and an outer jacket surrounding and co-axial with the inner line wherein a static vacuum is established within an elongate annular space between the inner line and outer jacket to limit heat input by conduction or convection. The space is typically also filled with an insulating substance such as aluminized mylar with alternating layers of glass paper or an equivalent in order to restrict heat input by radiation. It is also common to use cryogenic bayonet joints or connections to join sections of cryogenic pipe together in a field environment to minimize heat loss at such a connection. Known bayonet connections utilize a male insertion joint and a corresponding female receiving joint surrounding and co-axial with vacuum insulated inner lines to minimize heat input at the connection. An extremely close fit between the corresponding male and female joints defines a very thin annular cavity between the joints and the cryogenic fluid forms a vapor trap in the annular cavity to prevent loss of the fluid, and to restrict heat input through the joint. Known bayonet joints thereby provide an efficient structure for joining sections of cryogenic pipe in a field environment without any need for welding the pipes or any need for producing or reestablishing a static vacuum in the pipes. However, such bayonet joints are only for fixed sections of cryogenic pipes because the joints do not enable the sections of cryogenic pipe to rotate or swivel relative to each other.
To dispense fuel to a vehicle, a cryogenic fuel dispensing arm must be able to readily extend from a pump control housing to a dispensing position having a discharge outlet adjacent the vehicle and then move safely back to the control housing into a stored position. For such a cryogenic fuel dispensing arm to perform efficiently such a task, it must include one or more joints that permit swiveling of pipe sections relative to each other.
Typical non-cryogenic swivel joints, however, involve mechanical components such as bearing races and seals that are in close proximity to the process fluids passing through the joint. If the fluids were to be at temperatures common to cryogenic fluids, standard elastomeric seals would become brittle and could fail, and common bearing lubricants could not be used. Moreover, rapid temperature fluctuations of mechanical components of the joint that are metal when the components transition from ambient temperatures to extremely cold temperatures could cause contraction and cracking of such components, and subsequent leakage. Additionally, even if specialty metals, and cold temperature seals and lubricants were used, traditional swivel joints would still remain a source of heat input to the cryogenic fluid, and thereby decrease overall efficiency of an LNG dispensing station using such a swivel joint. No known swivel joint for a fluid transferring or conducting system is able to both effectively restrict heat input into the fluid and also maintain mechanical components of the joint at ambient temperatures while a cryogenic process fluid passes through the joint.
Accordingly it is a general object of the present invention to provide a swivel bayonet joint for cryogenic fluids that overcomes the deficiencies of the prior art.
It is more specific object to provide a swivel bayonet joint for cryogenic fluids that enables hardware components of the joint to remain at ambient temperatures while a cryogenic fluid passes through the joint.
It is another specific object to provide a swivel bayonet joint for cryogenic fluids that can be readily assembled in a field environment.
It is yet a further object to provide a swivel bayonet joint for cryogenic fluids that enables sections of cryogenic pipe connected by the joint to swivel while the cryogenic fluid passes through the joint.
The above and other advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.